33 



The indices over the NL-TR survey area ranged widely in value (1.0-9.0; Figure 3- 

 19) indicative of a patchy benthic environment. The frequency distribution of the median 

 OSI values at the disposal site indicated that the majority of stations had OSI values of 8.0 

 and 6.0 (Figure 3-20). OSI values were highest near the NL-TR survey center. This result 

 may be related to the reworking of the sediment by reburrowing Stage III adult organisms 

 with the fresh source of dredged material. Reference area OSI values had a narrower 

 uniform range (4 to 7.5) than at the NL-TR stations. Overall, the mean OSI value of the 

 NL-TR survey area were greater than the mean value of the reference areas, therefore, the 

 null hypothesis was rejected (p=0.05, Mann-Whitney U-test; Figure 3-20). The number of 

 indeterminate successional stages at the WREF (in addition to indeterminate RPD values) 

 decreased the number of OSI values calculated for this reference area. 



3.3 Sediment Analysis 



3.3.1 Grain Size and Total Organic Carbon 



The results of the sediment grain size (Table 3-1) analysis corresponded well with the 

 mapped distribution of sediment grain size as determined from REMOTS® photographs 

 (Figure 3-6). The sediments were typically dark gray sands with shell fragments present in 

 sediments from NE-REF and NLON-REF. Fine sands (4-2 phi) were dominant with a mix 

 of silt and clay (>4 phi) at all three areas. Silt made up a larger proportion of the >4 phi 

 fraction at NE-REF and NLON-REF while silt and clay were equally distributed at the 

 WREF. Total organic carbon was 0.48% at WREF, 0.50% at NE-REF, and 0.39% at 

 NLON-REF. 



3.3.2 Metals 



Cadmium, Pb, and Zn were detected at all reference areas (Table 3-2). Cadmium 

 values ranged from <0.05 to 0.22 ppm; lead from 13 to 30 ppm; and zinc from 28 to 

 64 ppm. Replicate values for each reference area were within approximately one standard 

 deviation of the mean (Table 3-2). The average values for Cd, Pb, and Zn were similar for 

 the three reference areas. 



3.3.3 PAHs 



Replicate values for each reference area were more variable for the organic 

 compounds than the metals; values fell within two standard deviations of the mean (Table 3- 

 3). Also, there were several estimated values (J values) that indicated a compound was 

 present in a concentration above the method detection limit and below the practical 

 quantitation limit. The method detection limit is based on results obtained from the method 

 blank processed with the samples. The practical quantitation limit is the lowest level of 



Monitoring Cruise at the New London Disposal Site, June 1991 



